1. Field of the Invention
The present invention relates to a process and apparatus for the removal of Total Reduced Sulfur compounds (TRS), especially H.sub.2 S and mercaptans, from industrial gases. More particularly, the present invention relates to a spray dryer absorption process employing an aqueous manganese dioxide suspension as an oxidative absorbent and preferably involves enhanced absorption by including a bag filter unit downstream of the spray dryer absorber.
2. Description of the Prior Art
Various processes have been proposed for reducing the content of sulfur compounds in industrial waste gases. Most of these processes relate to the removal of sulfur oxides. Because of their substantial acidic character, these sulfur oxides are readily absorbed by alkaline absorbents. Unfortunately, the same absorbents are not generally satisfactory for removing a number of important industrial byproduct sulfur compounds such as hydrogen sulfide, mercaptans and other organic sulfur containing compounds, since the acidic character of these compounds is generally much less pronounced. This is particularly true of the mercaptans for which there is no effective removal process being used commercially.
In British patent specification No. 1,576,534 a process for removing hydrogen sulfide from a hot reducing gas is disclosed. The process uses an absorbent comprising a mixture of finely divided manganese oxide, i.e., manganese of oxidation state 2, and finely divided aluminum oxide. Both the absorption and regeneration steps of the patented process require gas temperatures substantially higher than those typically encountered in industrial applications, for example, in pulping mills. Furthermore, a hot sulfur oxide-containing gas is produced by the disclosed high temperature regeneration technique, creating additional disposal problems in many cases. Moreover, it does not appear that the absorbent can remove mercaptans from gas streams.
U.S. Pat. No. 3,898,320 to Atsukawa uses a dry, powdered absorbent comprising a hydrated manganese oxide to remove sulfur oxides from gas streams. As described, the sulfur oxides in the gas react with the hydrated manganese oxide absorbent to produce manganese sulfate. The manganese sulfate is subsequently solubilized in water, converted to manganese hydroxide in the presence of ammonium hydroxide and is thereafter reconverted to the hydrated absorbent by oxidation with an oxygen-containing gas. The oxidation is conducted by bubbling the oxygen-containing gas through an aqueous dispersion of the manganese hydroxide. As in the prior process, there is no indication that this absorbent can be used to remove H.sub.2 S or organic sulfur compounds, particularly mercaptans.
U.S. Pat. No. 3,492,083 to Lowicki, et al., describes a process for removing sulfur containing compounds including H.sub.2 S and organic sulfur compounds which employs a complex multicomponent absorbent. This absorbent includes a metal oxide, hydrated oxide or hydroxide or preferably mixtures thereof, for example, manganese dioxide and magnesium oxide, in combination with an alkali metal or alkaline earth metal oxide or hydroxide, for example, sodium hydroxide. The absorption process is conducted at a relatively low temperature but an oxidic roasting at an elevated temperature above at least about 750.degree. C. is required to regenerate the absorbent. As in the prior British patent, problems with disposing a high temperature regeneration gas containing sulfur dioxide are created in many cases.
It is an object of the present invention to provide a process and apparatus for efficiently removing H.sub.2 S and organic sulfur-containing compounds, and particularly mercaptans, from industrial gas streams.
It is another object of this invention to provide a process and apparatus for removing the aforementioned sulfur compounds from industrial gas streams that permits a smooth and continuous operation suitable for automation.
It is a further object of this invention to provide a process for removing these sulfur compounds from industrial gas streams which employs a readily available absorbent that can be simply and efficiently regenerated by ambient temperature oxidation procedures.